The invention relates to a system for supplying voltage to electrical loads in the onboard electrical system of a motor vehicle.
In the case of known systems, the generator required for generating the voltage consumes a considerable amount of power, which has to be made available by the engine of the motor vehicle.
It is an object of the present invention to reduce the power to be provided by the motor vehicle engine for supplying the onboard electrical system of the motor vehicle with sufficient electric energy.
This object is achieved by a system for supplying the voltage to electrical loads in the onboard electrical system of a motor vehicle, wherein the onboard electrical system includes at least two onboard electrical system regions. The first onboard electrical system region has an electric generator, a vehicle battery, as well as one or more first electrical loads. The second onboard electrical system region has an energy accumulator, in particular, a capacitor, and one or more second electrical loads. Between the two onboard electrical system regions, a blocking device is provided, in particular, a semiconductor diode or a power switch, which permits a current flow from the first onboard electrical system region into the second onboard electrical system region and largely prevents a reverse current flow from the second onboard electrical system region into the first onboard electrical system region. The output voltage of the electric generator is raised and the capacitor is charged when there is a falling below a first threshold value of the electric voltage in the second onboard electrical system region. Advantageous embodiments of the invention are described herein.
According to the invention, the electrical loads in the onboard electrical system of a motor vehicle are divided into a group of at least two types of electrical loads. The first group of electrical (non-sensitive) loads will also operate reliably when there are relatively wide voltage fluctuations and/or when the voltage is relatively low; for example, when, in the case of a 12 volt onboard electrical system, the voltage falls below 10 volts and/or fluctuates between approximately 9 and 16 volts.
In contrast, the second group of electrical (sensitive) loads will operate reliably only when there are relatively slight voltage fluctuations about the nominal voltage; for example, when, in the case of a 12 volt onboard electrical system, the voltage fluctuates only between approximately 11 and 13 volts. According to the invention, the onboard electrical system is divided into at least two electrical system regions; the non-sensitive electrical loads are arranged in the first electrical system region, and the sensitive electrical loads are arranged in the second electrical system region.
A current flow from the second onboard electrical system region into the first onboard electrical system region, according to the invention, is largely prevented by a blocking device or circuit, preferably a semiconductor diode arranged between the first and the second electrical system regions. In the first onboard electrical system region, the electric generator and a vehicle battery are arranged in parallel to the first electrical loads, and in the second onboard electrical system region, an energy accumulator, a battery or a capacitor, preferably a double-layer capacitor or a so-called supercap, is arranged in parallel to the second electrical loads. During operation of the motor vehicle, the double-layer capacitor is regularly charged to a voltage which keeps the sensitive second electrical loads ready to operate while the capacitor discharges.
During the phases in which the double-layer capacitor does not have to be charged, the voltage of the generator is reduced to such an extent that the operational readiness of the first electrical loads (still) exists (see DE 2006 002 985). In this case, the voltage at the double-layer capacitor is higher than at the first (non-sensitive) loads, and the blocking device or diode prevents the discharge of the double-layer capacitor by way of the loads of the first onboard electrical system region. Inversely, the blocking device permits an electric current flow from the electric generator by way of the blocking device or diode into the second onboard electrical system region when the output voltage of the generator is raised in order to charge the double-layer capacitor.
The monitoring of the charge condition or of the output voltage of the double-layer capacitor takes place by way of a charge control device, which controls the generator such that, when the capacitor voltage falls below a threshold voltage, the generator increases the voltage for charging the capacitor and then subsequently reduces the voltage again.
In contrast to the known state of the art, the generator can be controlled such that, during operation of the motor vehicle, it predominantly provides only a lower voltage for operating the non-sensitive loads. In the case of the known state of the art, it was, however, necessary to increase the voltage to such an extent and duration that even the sensitive loads always had a sufficient operating voltage available.
Thus, according to the invention, the power consumption of the generator can be reduced for long periods of time and the fuel consumption and the CO2 emission of the motor vehicle can thereby clearly be reduced.
In a preferred embodiment of the invention, the time duration and/or the amount by which the electric voltage is raised in the second onboard electrical system region is a function of the energy consumption of one or more second electrical loads and/or of the capacitance of the capacitor in the second onboard electrical system region.
As an alternative or in addition, it is provided in a further preferred embodiment of the invention that the time duration and/or the raised voltage amount is proportional to the energy consumption of the one or more second electrical loads and/or proportional to the capacitance of the capacitor.
As a result of these measures, the charging operation can be optimized, particularly with respect to a further reduction of the CO2 emission.
In another preferred embodiment of the invention, it is provided that, for their operation, the first electrical loads require an operating voltage which is in a first voltage range and, for their operation, the second electrical loads require an operating voltage which is in a second operating range. The second voltage range preferably is narrower than the first voltage range; i.e., in contrast to the first electrical loads, the second electrical loads are so-called sensitive electrical loads of the motor vehicle.
As an alternative or in addition, it is provided in a preferred embodiment of the invention that the non-sensitive first electrical loads are largely provided in the first onboard electrical system region and the sensitive second electrical loads are largely provided in the second onboard electrical system region of the motor vehicle.
As a result of this measure, the invention can be technically implemented in a particularly simple manner.
In the case of a concrete embodiment of the invention for a classic 12 volt onboard electrical system, the voltage range predominant in the first onboard electrical system region during the operation of the vehicle comprises a voltage of approximately 10 to 16 volts, and the voltage range predominant in the second onboard electrical system region during the operation of the vehicle comprises a voltage of approximately 11 to 13 volts.
In a further embodiment of the invention, it is provided that, after the operation of the vehicle, the capacitor is separated from the second onboard electrical system region, is then preferably discharged and charged again during another operation of the vehicle, and is electrically connected with the onboard electrical system region and is charged.
As a result, the reliability of the onboard electrical system is increased in the event of short circuits, and the high quiescent current of supercapacitors (supercaps or SCs) is avoided in the stationary phases. The precharging and the coupling/uncoupling of the supercap to/from the onboard electrical system preferably takes place by a separate control/power unit which, preferably simultaneously, carries out the diagnosis of the SC (such as the determination of the capacitance and resistance during the precharging operation).
In a preferred embodiment of the invention, it is provided that the accumulator in the second electrical system is a battery or, preferably, a capacitor such as a double-layer capacitor or a so-called supercap.
Such capacitors are distinguished by high charge densities, so that high capacitances can be provided while keeping the dimensions small. Further, such capacitors can be charged rapidly at high currents, which is advantageous with respect to a reduction of CO2.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.